The present disclosure relates to a modular multi-level converter, and more particularly to, a modular multi-level converter capable of effectively controlling a plurality of sub-modules.
High voltage direct current (HVDC) transmission refers to an electric power transmission method in which alternating current (AC) power generated from a power plant is converted into direct current (DC) power and transmitted by a transmission substation, after which the transmitted DC power is converted into AC power again at a receiving substation to supply the power.
HVDC systems are applied to undersea cable transmission, high-capacity long distance transmission, interconnections between AC systems, and the like. Also, HVDC systems make possible interconnections between different frequency system and asynchronous interconnections.
A transmission substation converts AC power into DC power. That is, since the transmission of AC power by using an undersea cable or the like presents a very dangerous situation, the transmission substation converts AC power into DC power to transmit to the receiving substation.
Meanwhile, there are various types of voltage-type converters used in HVDC systems, and modular multi-level voltage-type converters have recently attracted the most interest.
A modular multi-level converter (MMC) is an apparatus which converts DC power into AC power by using a plurality of sub-modules, and operates such that each of the sub-modules are controlled to be in states of charge, discharge, or bypass.
Accordingly, in an MMC, it is most important to control the plurality of sub-modules in the power converting operation, and the control operation of the plurality of sub-modules determines the form and quality of output AC power.
Thus, an MMC capable of efficiently controlling the plurality of sub-modules of the MMC is required.